The lead content of many tissues is directly proportional to lead exposure. However, experimental studies show that dose-and time-dependent nonlinearities between dose rate and kidney lead content occur in the rat. Furthermore, epidemiological and experimental studies have demonstrated that blood lead concentration shows a decreasing incremental rise with increasing exposure in both rats and humans. This study is designed to: 1) investigate the subcellular distribution of lead in the kidney as a function of duration and magnitude of exposure, 2) correlate these data with the results of tolerance studies to determine redistribution and sequestration are mechanisms of tolerance development, and 3) attempt to identify a renal effect of lead at the functional level which may be associated with an active fraction of kidney lead.